Edit File: queue.h
/* * Copyright (C) Internet Systems Consortium, Inc. ("ISC") * * This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, you can obtain one at https://mozilla.org/MPL/2.0/. * * See the COPYRIGHT file distributed with this work for additional * information regarding copyright ownership. */ /* * This is a generic implementation of a two-lock concurrent queue. * There are built-in mutex locks for the head and tail of the queue, * allowing elements to be safely added and removed at the same time. * * NULL is "end of list" * -1 is "not linked" */ #ifndef ISC_QUEUE_H #define ISC_QUEUE_H 1 #include <stdbool.h> #include <isc/assertions.h> #include <isc/mutex.h> #ifdef ISC_QUEUE_CHECKINIT #define ISC_QLINK_INSIST(x) ISC_INSIST(x) #else #define ISC_QLINK_INSIST(x) (void)0 #endif #define ISC_QLINK(type) struct { type *prev, *next; } #define ISC_QLINK_INIT(elt, link) \ do { \ (elt)->link.next = (elt)->link.prev = (void *)(-1); \ } while(0) #define ISC_QLINK_LINKED(elt, link) ((void*)(elt)->link.next != (void*)(-1)) #define ISC_QUEUE(type) struct { \ type *head, *tail; \ isc_mutex_t headlock, taillock; \ } #define ISC_QUEUE_INIT(queue, link) \ do { \ (void) isc_mutex_init(&(queue).taillock); \ (void) isc_mutex_init(&(queue).headlock); \ (queue).tail = (queue).head = NULL; \ } while (0) #define ISC_QUEUE_EMPTY(queue) ((queue).head == NULL) #define ISC_QUEUE_DESTROY(queue) \ do { \ ISC_QLINK_INSIST(ISC_QUEUE_EMPTY(queue)); \ (void) isc_mutex_destroy(&(queue).taillock); \ (void) isc_mutex_destroy(&(queue).headlock); \ } while (0) /* * queues are meant to separate the locks at either end. For best effect, that * means keeping the ends separate - i.e. non-empty queues work best. * * a push to an empty queue has to take the pop lock to update * the pop side of the queue. * Popping the last entry has to take the push lock to update * the push side of the queue. * * The order is (pop, push), because a pop is presumably in the * latency path and a push is when we're done. * * We do an MT hot test in push to see if we need both locks, so we can * acquire them in order. Hopefully that makes the case where we get * the push lock and find we need the pop lock (and have to release it) rare. * * > 1 entry - no collision, push works on one end, pop on the other * 0 entry - headlock race * pop wins - return(NULL), push adds new as both head/tail * push wins - updates head/tail, becomes 1 entry case. * 1 entry - taillock race * pop wins - return(pop) sets head/tail NULL, becomes 0 entry case * push wins - updates {head,tail}->link.next, pop updates head * with new ->link.next and doesn't update tail * */ #define ISC_QUEUE_PUSH(queue, elt, link) \ do { \ bool headlocked = false; \ ISC_QLINK_INSIST(!ISC_QLINK_LINKED(elt, link)); \ LOCK(&(queue).taillock); \ if ((queue).tail == NULL) { \ UNLOCK(&(queue).taillock); \ LOCK(&(queue).headlock); \ LOCK(&(queue).taillock); \ headlocked = true; \ } \ (elt)->link.prev = (queue).tail; \ (elt)->link.next = NULL; \ if ((queue).tail != NULL) \ (queue).tail->link.next = (elt); \ (queue).tail = (elt); \ UNLOCK(&(queue).taillock); \ if (headlocked) { \ if ((queue).head == NULL) \ (queue).head = (elt); \ UNLOCK(&(queue).headlock); \ } \ } while (0) #define ISC_QUEUE_POP(queue, link, ret) \ do { \ LOCK(&(queue).headlock); \ ret = (queue).head; \ while (ret != NULL) { \ if (ret->link.next == NULL) { \ LOCK(&(queue).taillock); \ if (ret->link.next == NULL) { \ (queue).head = (queue).tail = NULL; \ UNLOCK(&(queue).taillock); \ break; \ }\ UNLOCK(&(queue).taillock); \ } \ (queue).head = ret->link.next; \ (queue).head->link.prev = NULL; \ break; \ } \ UNLOCK(&(queue).headlock); \ if (ret != NULL) \ (ret)->link.next = (ret)->link.prev = (void *)(-1); \ } while(0) #define ISC_QUEUE_UNLINK(queue, elt, link) \ do { \ ISC_QLINK_INSIST(ISC_QLINK_LINKED(elt, link)); \ LOCK(&(queue).headlock); \ LOCK(&(queue).taillock); \ if ((elt)->link.prev == NULL) \ (queue).head = (elt)->link.next; \ else \ (elt)->link.prev->link.next = (elt)->link.next; \ if ((elt)->link.next == NULL) \ (queue).tail = (elt)->link.prev; \ else \ (elt)->link.next->link.prev = (elt)->link.prev; \ UNLOCK(&(queue).taillock); \ UNLOCK(&(queue).headlock); \ (elt)->link.next = (elt)->link.prev = (void *)(-1); \ } while(0) #define ISC_QUEUE_UNLINKIFLINKED(queue, elt, link) \ do { \ LOCK(&(queue).headlock); \ LOCK(&(queue).taillock); \ if (ISC_QLINK_LINKED(elt, link)) { \ if ((elt)->link.prev == NULL) \ (queue).head = (elt)->link.next; \ else \ (elt)->link.prev->link.next = (elt)->link.next; \ if ((elt)->link.next == NULL) \ (queue).tail = (elt)->link.prev; \ else \ (elt)->link.next->link.prev = (elt)->link.prev; \ } \ UNLOCK(&(queue).taillock); \ UNLOCK(&(queue).headlock); \ (elt)->link.next = (elt)->link.prev = (void *)(-1); \ } while(0) #endif /* ISC_QUEUE_H */
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